Fuel injection pump



June 13, 1944. H; o. FARMER 2,351,414

FUEL INJECTION PUMP Filed Jan. 28, 1941 \NvENToE;

Patented June 13, 1944 FUEL INJECTION PUMP Harold Oatridge Farmer, Hounslow, England, as

sig-nor to Alan Muntz 80 Company Limited, Hounslow, England, a company of Great Britain Application January as, 1941', Serial. No. 376359 In Great Britain February 13,. 1940- 4 Claims.

This invention relates to pumps for injectin liquid fuel intermittently to the combustion cham- .bers of internal-combustion engines, the pumps being of the kind in which the movement of the pump plunger is not controlled by positively acting mechanical means throughout the cycle of operation and in which therefore the plunger is liable to excessive displacement at the end of the delivery stroke. Such excessive displacement is D apt to caus shock to the reciprocating parts of the pump, and this difficulty is especially evident with certain kinds of pumps, for example those in which the plungers are operated by means such as pistons (which are distinct from the main pistons of the engine) acted upon by the pressure of the gas in the working cylinders, and with .pumps required to operate at high cyclical speeds.

An object of this invention is to provide means for controlling the movement of the plunger of a fuel pump at the end of the injection period.

Another object is to enable the same means to limit the movement ofthe plunger atthe end of its suction stroke.

In the embodiment of the invention, hereinafter described by way of example, the pump is of the kind in which the plunger is operated by a piston or equivalent means acted upon b the pressure of gas in the working cylinder of the engine, and the pump plunger is operatively associated with a return spring so arranged that its stiffness increases with movement of the plunger in the fuel-injecting direction. This example will be described with reference to the accompanying drawing, in which- Fig. 1 is a side elevation, partly in section, of the pump proper and the operating mechanism, and

Fig. 2 is a plan of the spring.

A. pump of usual type, including a barrel in which a plunger is slidable, is generally denoted,

by In in Fig. 1. A casing H, to which the pump Ill is rigidly fixed by means not shown, contains a bore 12 in which is slidably fitted a gas-operated piston l3. The actuating member i i of the pump ID which incorporates a conventional plunger return spring (not shown) is operatively connected to the gas-operated piston l3 by means of an adjustable tappet l5 mounted in the upper end of the piston 13'. The lower end of the bore i2 is closed by a cover [6 fitted with a pipe union ll adapted to be connected to the combustion chamber of the engine cylinder. The casing l l is provided with a box-like projection l8 closed by a cover l9 and extending perpendicularly to the axis of the bore l2. A tapered leaf spring 20 of the laminated cantilever type, a plan view of which appears in Fig, 2, is disposed in the projection I8, its broad end being clamped to the upper wall 01' the projection I-8 by two screws 2| and a cap plate 22. A stop member 23 is also clamped by the screws 2| between the spring 20 and the said wall, the lower surface of the stop member being curved upwards towards the end thereof nearer to the bore I2, as shown'at 2-4. The narrow, free end of the spring 20 is provided with a cap 25 of part-cylindrical section which is accommodated within a transverse slot 26 machined in the piston l3.

The parts are shown in the positions which they occupy when the pressure in the combustion chamber of the engine, and therefore the pressure under the gas piston I3, is substantially atmospheric. Under these conditions that part of the spring 20 adjacent to the curved part 24 of the stop member 23 is spaced from th latter so that the effective length of the spring is the maximum and its stiffness (i. e. ratio of load increment to deflection increment) is consequently the minimum. During the compression stroke of the engine, as the gas pressure under the piston l3 increases, this piston rises and deflects the free end of the spring upwards, with the result that an increasing length of the spring bears on the stop member 23 along the curved surface 24. Thus the efiective length of the spring is progresiection the pressure on the fuel-pump plunger is suddenly released while the gas pressure under the piston 13 is at or near its maximum value. .Since however at this stage the stiffness of the spring it is relatively very large, the spring is able to resist the heavy load imposed on it and so prevent excessive movement of the gas piston .63 and the pump plunger. After the pressure in the combustion chamber of the engine has fallen during the expansion stroke and the pump plunger has completed its suction stroke, the spring 29, operating now with uniform stiiiness as it is deflected downwards from the neutral position shown, limit excessive downward movement by said leaf spring and increase the stiffness of the spring as its deflection increases.

2. A pump for injecting liquid fuel intermittently into the combustion chamber of an internal combustion engine, said pump including a body comprising a gas cylinder having'a port for communication with the engine combustion chamber, a gas piston slidable in said cylinder for cooperation with the fuel-injecting plunger of the pump in such a manner that admission of gas under pressure to said cylinder causes said pump to make an injection stroke, and a spring one part of which is rigidly anchored to said body and another part of which is coupled to said gas piston by means capable of deflecting said spring to both sides of its neutral position, said spring having an increasing ratio of load increment to deflection.

increment when deflected by displacement of said gas piston in the fuel-injecting direction, and said spring being capable of checking movement of said plunger and said gas piston at the end of the suction stroke of said plunger.

with said spring on deflection in the direction corresponding to the fuel-injection. stroke of said pump for increasing the ratio of load increment to deflectionincrement as deflection in said direction increases, said spring being capable of checking movement of said reciprocable member in the opposite direction.

.' 4. Aplunger pump for injecting liquid fuel intermittently into the combustion chamber of an internal combustion engine, said pump being of the type in which the liquid fuel pressure on the pump plunger is suddenly released at the end of the fuel-injectionoperiod, and said pump including a body comprising a gas chamber having a port communicating with the engine combustion chamber, a wall element of said chamber being slidably guided in said body for cooperation with said plunger in such a manner that admission of gas under pressure to said chamber causes 20 said pump to make an injection stroke, and a spring disposed between-said wall element and said body and having a ratio of load increment to deflection increment which increases when the spring is deflected by displacement of said 25 wall element in the fuel injecting direction, said stroke, a spring mounted in an anchorage rigid with the body of said pump and coupled to said reciprocabie member for deflection to both sides of the neutral position, and means cooperating spring serving as the only abutment means for .limiting such displacement of said wall element so that the wall element is protected from impact with said body on said release of liquid fuel pres- 3 sure. 

